**1.5. Feeding, diet and diving behaviour**

South American fur seals have mainly pelagic feeding habits (Naya et al., 2002; Ponce de León & Pin, 2000, 2006; Vaz-Ferreira, 1976) but also feed in shallower waters (Franco-Trecu, 2010). Their diet is basically composed of anchovies (*Engraulis anchoita, Anchoa marinii*), squid (*Illex argentinus, Loligo sanpaulensis*), hake (*Merluccius hubbsi*), striped weakfish (*Cynoscion guatucupa*), oceanic shrimp (*Pleoticus muelleri)* and cutlassfish (*Trichiurus lepturus*) (Frau & Franco-Trecu, 2010; Naya et al., 2002; Pin et al., 1996; Ponce de León et al., 1988; Ponce de León et al., 2000; Ponce de León & Pin, 2006; Vaz Ferreira 1976; Vaz-Ferreira & Ponce de León, 1984, 1987). Uruguayan fur seals usually do not interfere directly with artisanal and industrial fisheries, as they do not eat from nets nor destroy fishing gears (Ponce de León & Pin, 2006), though there are a few records of fur seal by-catch in artisanal (Franco-Trecu et al., 2009) and industrial fisheries (Szephegyi et al., 2010).

156 New Approaches to the Study of Marine Mammals

Lobos Island and Lobos Islet.

**1.5. Feeding, diet and diving behaviour** 

Trecu & Trimble, unpublished data). Territorial males display violent fights that may last at least one hour, and end with serious wounds. After parturition, sea lion females remain with their pups in order to suckle them for approximately one week and then start short foraging trips of three days, alternated with two-day suckling periods on land (Campagna & Le Boeuf, 1988). There is a decrease in the number of adult males and females at the end of the reproductive season because, after fasting during the breeding season, males begin their foraging period at sea. In addition, adult females alternate foraging trips at sea and suckling periods ashore, and move to other areas of the island (Franco-Trecu & Trimble, unpublished data; Ponce de León & Pin, 2006). Despite the fact that sea lions abandon the islands in order to move to feeding areas, there are generally some animals in the rookeries, even outside the reproductive season. In many other South American colonies this species maintains an increasing population growth (Grandi et al., 2008; Sepúlveda et al., 2006) and has been classified as low risk by the IUCN. However, sea lions in Uruguay are considered a highly endangered species due to their population decrease of 1.7 to 2% annually, with a total

population estimated at only 12.000 individuals (Páez, 2006; Pedraza et al., 2009).

On Lobos Island and Lobos Islet, South American sea lion groups are found in small patches, surrounded by large groups of South American fur seals. However, on the Torres Islands (Rasa Island, Encantada Island and Islet), Marco Island and other islets, groups of sea lions are more numerous than on the bigger Lobos Island. According to Pedraza et al., (2009) and Ponce de León (unpublished data), sea lion populations are stable or increasing (2.4% annually) in Polonio´s Cape islands, while in Lobos Island their growth have a negative tendency. This is related to a positive trend in the *A. australis* population and may be an indicator of competition for territory (breeding areas), a process that occurs only on

The breeding and reproductive areas of the elephant seal *Mirounga leonina* are located in sub Antarctic regions along the coast of South America (Campagna & Lewis, 1992; Lewis et al*.,* 1998) and smaller colonies are formed in the Antarctic (Le Boeuf & Laws, 1994). The only large breeding colony of southern elephant seals on the South American continent is found in Península Valdés (42°04'S, 63°45'W) (Campagna & Lewis, 1992; Le Boeuf & Laws 1994; Lewis et al., 2004). Young, juvenile and adult animals migrate to northern regions (Lewis et al., 2006) and occur at different points all along the Uruguayan shoreline of the La Plata River and Atlantic Ocean beaches. During practically the whole year, elephant seals of both sexes are frequently seen in the flat areas of access to Lobos Island, Lobos Islet, Rasa Island and Coronilla Islet (Fig. 3 and 4). Mother and pup couples have been seen on Lobos Island in October, and in some odd cases, individuals have swum up the waters of the Uruguay

River to the Departments of Rio Negro and Paysandú (Ponce de León & Pin, 2000).

South American fur seals have mainly pelagic feeding habits (Naya et al., 2002; Ponce de León & Pin, 2000, 2006; Vaz-Ferreira, 1976) but also feed in shallower waters (Franco-Trecu, 2010). Their diet is basically composed of anchovies (*Engraulis anchoita, Anchoa marinii*), Diving records obtained by different researchers showed that during lactation, female fur seals perform dives of up to 186 m (media: 23.5 m ± 19.5 m) in depth with an average duration of 1.2 min ± 0.8 min (max. 5.3 min.) (Riet et al., 2010; York et al., 1998). These data suggest that females use both benthic and pelagic foraging strategies, and demonstrate their huge endurance for deep dives, apnea resistance and swimming ability. Diurnal dives were shallower and shorter than nocturnal ones (Riet et al., 2010). It was determined that lactating females consume different prey species, adapting their diving strategies to variations in food resources (Ponce de León & Páez, 1996; Ponce de León & Pin, 2006; Riet et al., 2010; York et al., 1998).

During early lactation, female sea lions perform dives of 21 m ± 8 m in depth with an average time of 1.9 min ± 0.7 min. Mean distance traveled per trip was 62.2 km ± 63.0 km. Foraging trips lasted 1.3 ± 0.8 days and did not exceed the continental shelf (>50 m of depth). Maximum distance from the colony was 98.60 km ± 31.3 km. These results indicate that during the breeding season females forage in coastal and shallow continental shelf areas (Riet et al., 2009, 2012). In autumn, foraging trips last 5 days (range: 1-14 days). Most animals seemed to complete round trips along the same tracks, meaning that each animal uses the same path on successive trips, with low overlap between individuals. Site fidelity to Lobos Island was highly remarkable for all animals, independently of their reproductive condition (Rodríguez et al., 2012).

Sea lions compete directly with small-scale coastal fishing and artisanal fisheries, feeding on species that are part of the fishermen's daily catch by stealing prey trapped in nets and longlines, and sometimes causing important damage or cracks in the gear (Franco-Trecu et. al., 2012; Lezama & Szteren, 2003; Ponce de León & Pin, 2006; Szteren & Páez, 2002). According to different authors, the sea lions' diet is mainly made up of coastal prey and some pelagic fishes: whitemouth croaker *(Micropogonias furnieri)*, striped weakfish (*Cynoscion guatucupa*), Brazilian codling (*Urophysis brasiliensis*), cutlassfish (*Trichiurus lepturus*), mackerel (*Trachurus lathami*), Argentinean conger (*Conger orbignyanus*), carangid (*Parona signata*), two species of anchovies (*Engraulis anchoita* and *Anchoa marinii*), and Argentinean croaker (*Umbrina canosai*) (Franco-Trecu, 2010; Naya et al., 2000; Pinedo & Barros, 1983; Ponce de León & Pin, 2006; Riet et al., 2011, 2012; Vaz Ferreira, 1981). As a consequence of interactions with sea lions, fishermen lost prey with high local commercial market value. Sometimes, fishermen find small shark specimens in their nets (*Mustelus schmitti, Galeorhinus galeus, Myliobatis* spp.) which have bite marks in their abdominal area

(Fig. 5) from sea lions that learned to exploit this energy reservoir (Ponce de León & Pin, 2006). Recent reports show that during the early lactation period, foraging home ranges of sea lion females overlapped with fishing effort areas of coastal bottom trawl fisheries (15%) and artisanal fisheries (>1%). For both fisheries the resource overlap per fisheries impact index identified the "hotspots" which are distributed along the coast, west of the breeding colony (56ºW - 55Wº) (Riet et al., 2011).

Uruguayan Pinnipeds (*Arctocephalus australis* and *Otaria flavescens*): Evidence of Influenza Virus and *Mycobacterium pinnipedii* Infections 159

theme parks all over the world. The principal objective of these parks is to educate people about environmental issues and about the conservation of aquatic and marine resources and ecosystems. Although live sea lions had been sold by the Uruguayan Government since 1980, the exportation of living specimens of this Otariid was suspended in 2006 by DINARA-MGAP due to decreasing population numbers. Captures of animals are held in Lobos Island from mid March to mid November. This special period was defined in order to avoid disturbances and to be respectful of parturition, breeding and mating periods of the two Otariid species present in the island (Ponce de León, 2000; Ponce de León & Pin, 2006).

As far as research is concerned, DINARA maintains the old seal factory plant on Lobos Island, using parts of the buildings for providing accommodation to researchers who are developing studies in both species. Through the development of various research projects, the Government institution DINARA, students and graduates of the University of Uruguay (Universidad de la República) as well as from foreign countries, are gathering and collecting data to increase knowledge about the population dynamics of both species, which will also help in developing appropriate rules and guidelines for their management, and ensuring the

**2. Evidence of influenza virus infections in** *Arctocephalus australis*

Marine mammals are susceptible to a variety of pathogens including influenza viruses. In humans, influenza causes annual epidemics and occasional pandemic diseases, with a significant threat to human health. In wild animals, several outbreaks have been reported and especially marine mammals experienced several devastating episodes that highlight the importance of monitoring wild populations to perform conservation programs and to

Influenza viruses belong to the *Orthomyxoviridae* family and are enveloped viruses with a segmented, negative-sense RNA genome (Webster et al., 1992). Embedded in the lipid envelope, the hemagglutinin (HA) and neuraminidase (NA) proteins are responsible for virus attachment and release from host cells, respectively (Webster et al., 1992). This family of viruses is composed of four genera: influenza A, B and C viruses and Thogoviruses (Wright & Webster, 2001). While influenza B and C viruses are primarily "human" viruses, influenza A viruses infect a variety of avian and mammalian species including humans, horses, swine and marine mammals such as seals and cetaceans (Wright & Webster, 2001; Webster et al., 1992). Influenza B virus was isolated from a harbor seal (*Phoca vitulina*) for the first time in the year

Influenza viruses are unique among respiratory tract viruses as they undergo considerable antigenic variation. Both surface antigens of the influenza A viruses are subject to two types of variation: drift and shift. Antigenic drift involves minor changes in the hemagglutinin (HA) and neuraminidase (NA) and plays a role in influenza epidemics, which occur sporadically. Antigenic shifts involve major changes in these molecules resulting from

2000 (Osterhaus et al., 2000) becoming a possible second reservoir of this virus.

conservation of Uruguayan natural resources.

evaluate possible risks to human health.

**individuals** 

**Figure 5.** Artisan fishery capture of *Mylobatis* spp. The opened abdominal areas of the sharks are seen, from where sea lions have taken highly nutritive and energy rich livers and pancreas. Photograph: A. Ponce de León.
